This invention relates to coaxial cable equipment and more particularly to a coaxial heat sink connector.
The power handling capability of radio frequency (RF) components is significantly affected by the design of interconnecting coaxial RF cables (xe2x80x9ccoaxxe2x80x9d), which are widely used to connect RF components due to their large bandwidth capabilities. Heat dissipated in RF cables is generally transferred to the environment through radiation from the RF cable, and through conduction from the ends of the RF cable to the cable-connected RF components. In ground applications, convection helps reduce cable temperatures and accordingly, center conductor temperatures. In the case of electronic components for use in space applications, since there is no mechanism for convective heat transfer from the outer cable surfaces, other means of providing heat dissipation must be considered.
Generally, the length, design, and power level of the RF cables have a significant impact on the power-handling capability of RF components. This is especially the case in the thermal design of RF components for space applications, as the worst-case temperatures, de-rated power levels and worst-case dissipation specifications combine to ensure that temperature predictions bound any kind of flight applications. Fault conditions become especially difficult to design for, as typical fault scenarios result in full reflection of RF power through the RF cables, the RF cable connectors and the RF components. This full reflection can result in almost twice the rated power passing through an RF cable.
As shown in FIG. 1, RF cables 10 which are used in space applications are conventionally clamped to a heat sink (not shown) using a cable clamp 12. A heat sink is a device that is attached to heat generating equipment to prevent overheating by absorbing heat from the equipment and dissipating it into the immediate environment. This kind of assembly as shown in FIG. 1 provides a conduction point (i.e. at the cable clamp 12) for heat transfer from RF cable 10 and also ensures that RF cable 10 structurally adheres to a support structure. However, since the ends of RF cable 10 are too rigid to make suitable physical contact with cable clamp 12, cable clamp 12 must be positioned near the center of RF cable 10. Accordingly, this arrangement does not consistently sink heat from the center conductor of RF cable 10 and RF components.
In space applications, it is desirable to reduce the mass and equipment footprint of RF component assemblies and to reduce RF losses generally. By what is conventionally known as xe2x80x9cboltingxe2x80x9d together high power components using connectors instead of intermediate RF cables, several improvements can be realized. First, there is a substantial reduction of mass when components are bolted together as compared to when they are RF cabled together. As shown in FIG. 2, RF power components (e.g. circulators 14 and switches 16) are typically connected by long sections of RF cable 10 as long sections are required to minimize the thermal stress on RF cable 10 for durability and long life. Typically, each RF cable 10 is at least 6 inches (15.3 cm) long with each pair of cables having a typical mass of 45 grams. Moreover, when several pairs of these cables are used the cumulative mass can be appreciable. Also, there is an improvement in RF performance due to the absence of RF losses associated with an intermediate cable.
Further, when RF components are bolted together, the equipment footprint of the complete assembly is slightly larger than the cumulative footprint of the individual components (due to the short length of TNC connectors). In contrast, when RF cables are used between components, a suitable spacing is required to house the lengthy RF cables, and as a result the assembly has a larger overall footprint. Accordingly, the RF-cabled assembly takes up more room on a spacecraft, has a higher overall mass, and has a higher overall cost. FIG. 2 illustrates a spacecraft panel comprising of circulators 14 and switches 16 using RF cables 10 to interconnect flight components that could otherwise be bolted together. As shown, the width of a cable-connected panel layout is 16 inches (40.7 cm). In this case, the RF cables 10 that are used to attach circulators 14 to switches 16 are 5 inches (12.7 cm) long, and accordingly are a critical limiting factor for the overall panel width. Without the interconnecting cables, the width of this panel can be reduced by approximately 4 inches (10.2 cm).
However, when RF components are directly connected through connectors without the need for cables, the power-handling capability of the components is substantially reduced. First, when two high power components are bolted to each other, they interact with each other thermally (i.e. one component heats up the other). Also, RF cables provide radial heat transfer from the center conductor to the outer sheath, and when this radial thermal heat path is absent, the center conductors of the individual components become hotter than they would otherwise be, thus further limiting the power-handling capability of multiple power component assemblies. Also, conventional RF cable connectors are not designed to provide heat sinking functionality between RF components. Rather, RF cable connectors typically use a Teflon-based insulation layer between the center and outer conductors, which does not promote conduction of heat from the center conductor to the outer conductor due to its poor thermal conductivity.
The invention provides in one aspect, a heat sink connector for providing a heat transfer path from the conductors of a first coaxial cable connector to a heat sink, said heat sink connector comprising:
(a) a body comprising:
(i) a center conductor;
(ii) an outer conductor disposed around said center conductor;
(iii) an insulation layer positioned between said center conductor and said outer conductor, said insulative layer being selected to have a substantially high degree of thermal conductivity such that a substantial amount of heat is conducted from the center conductor to the outer conductor;
(b) a first connector positioned at one end of said body, said first connector being electrically coupled to said center conductor and said outer conductor, said first connector being adapted to electrically couple said center and outer conductors to the conductors of the first coaxial cable connector; and
(c) a thermal element coupled to the outer conductor, said thermal element having a surface adapted to be coupled to a heat sink such that said heat sink connector provides a heat transfer path from the conductors of the first coaxial cable connector to the heat sink through said center and outer conductors.
Further aspects and advantages of the invention will appear from the following description taken together with the accompanying drawings.